1. Technical Field of the Invention
The present invention relates to a current control interface arrangement including a card circuit and a connector means
2. Discussion of Related Art
Such a current control interface arrangement and more particularly the card circuit therein, is already known in the art, e.g. from the U.S. Pat. No. 5,283,707, by Conners et al, "Inrush current limiting circuit". Therein, an arrangement is described including a backplane having at least two conductors, a power supply connected to the conductors and a plurality of circuit cards attached to the backplane and connected to the conductors, whereby each of the plurality of circuit cards includes an inrush current limiting circuit. This inrush current limiting circuit includes input terminals for connection to a power supply output and to a reference potential, output terminals for connection to a load, an enable terminal for receiving an enable signal, and an active device having a control electrode and a conductive controlled path which is connected between the power input terminal and a respective one of the output terminals. A voltage supply means, connected to the enable terminal and the reference potential input terminal, and having an output for providing sufficient voltage to render the active device conductive, is included in the inrush current limiting circuit as well. This inrush current limiting circuit further includes a first time constant means, coupled between the voltage supply means and the control electrode, for controlling the rate at which the active device is rendered conductive in accordance with a predetermined time constant, and second time constant means coupled between the voltage supply means and the control electrode for rendering the active device non-conductive in accordance with a second predetermined time constant.
During hot insertion of the circuit card into the backplane, the active device conductive controlled path between its source and drain terminals is initially in a high impedance state. When an enable signal comprising a DC voltage, approximately equal to or less than 0.5 V DC below the level of the power supply input, being nominally 5 V DC, is applied to the enable input, the voltage supply is turned on and provides an output voltage of between approximately 10 to 12 V to the power-up time constant circuit, which then further controls the rate of change of the voltage applied to the control electrode of the active device, in the prior art solution being a n-type FET switch. During the extraction procedure of the circuit board from the backplane module first the enable input voltage is removed from the enable input. The power down time constant circuit discharges the control electrode of the active device, thereby controlling the rate of power supply unloading, after which the circuit board can be removed from the backplane.
The prior art solution with the enable functionality thus requires an extra externally controlled enable signal line per card, as well as a voltage supply on each card. The necessity to provide such an extra externally controlled enable signal on each card represents an extra cost. Similarly, the presence of such a voltage supply in the current limiting circuit, which is placed on each card, also implies an extra cost.